The invention relates to a gas-exhaust gas turbocharger for an internal combustion engine with variable turbine geometry.
DE 35 41 508 C1 discloses an exhaust-gas turbocharger, the exhaust-gas turbine of which is designed as a radial turbine which has a radial inflow passage through which exhaust gas flows via a radial flow inlet cross-section into the turbine section and onto a turbine wheel. A variable turbine geometry in the form of a guide vane ring with adjustable guide vanes, is arranged in the flow inlet cross-section. The guide vanes can be adjusted between a throttling position, which reduces the free flow inlet cross-section to the turbine wheel, and an open position, which widens the flow inlet cross-section as a function of the current operating state of the internal combustion engine. As a result the exhaust gas back pressure in the line section between the cylinder exhaust passage and the exhaust-gas turbine can be manipulated and set to a desired level. Exhaust-gas turbines of this type can be used both in the driving mode of the engine to increase the engine power and in the engine braking mode to generate engine-braking power.
Particularly in the engine-braking mode, the guide vanes are moved into the throttling position, in order to produce a high pressure level on both the exhaust-gas side and the air supply side in order to generate the desired high engine-braking powers. To make it possible to generate high exhaust-gas back-pressures, it is necessary to avoid incorrect air flows between the inlet passage of the turbine and the discharge side of the turbine. Undesirable incorrect air flows of this nature may be produced by gaps which may form in the region where the radial guide vanes are held in place at the end faces of the guide vanes, because of thermal and mechanical loads. Particularly in the case of commercial vehicle engines, which have to be able to generate a high engine-braking power, accurate mounting of the guide vanes combined, with a reduced thermal and mechanical load on the vanes is desirable in order to avoid incorrect air flows.
It is already known from U.S. Pat. No. 5,454,225 to provide a support wall, which is fixed to the casing, in the inflow passage of the exhaust-gas turbine. Although this support wall is fixedly connected to the turbine casing, it projects freely into the inflow passage. This support wall is used to support a variable turbine geometry in the radial flow inlet cross section to the turbine wheel. The support wall is of annular design, with the cross section of the support wall widening radially outwards. The variable turbine geometry is in the form of an adjustable guide vane structure in the radial flow inlet cross section. The guide vane structure is held, in the region of one of its end faces, on an outer casing wall and, in the region of its opposite end face, on the projecting-support wall.
Because of the widening of the cross section in the radial direction of the support wall, the support wall has a contour which is favorable for guiding the exhaust gas. The guide vane ring of the variable turbine geometry is mounted in the region of a narrow cross section of the support wall, directly adjacent to the radially outer end of the turbine wheel. The support wall is attached to the turbine casing by means of a semi-axial guide vane ring, via which exhaust gas can be fed to the turbine wheel in addition to the gas fed to the radial guide vane ring. With the guide vane ring, the supporting wall has a relatively high rigidity, which helps to transmit vibrations from the turbine casing to the supporting wall and to the variable turbine geometry. However, vibrations of this type, if they exceed an acceptable level, can adversely affect the operation of the variable turbine geometry.
It is the object of the invention to provide an exhaust-gas turbocharger, which has a high efficiency and a long service life.